Antennas are useful in a variety of data communications applications, including, for example, line-of-sight (LOS) communications applications, satellite communications (SATCOM), cellular telephony and digital personal communications systems (PCS). Antenna systems are often implemented as phased arrays of individual antennas or subarrays of antennas that are excited to cumulatively produce a transmitted electromagnetic wave that is highly directional, in order to provide a signal gain in a desired direction or to reject unwanted signals from other directions. The radiated energy from each of the individual antenna elements or subarrays is of a different phase, respectively, so that an equiphase beam front or cumulative wave front of electromagnetic energy radiating from all of the antenna elements in the array travels in a selected direction. Phase or timing differences among the antenna activating signals determines the direction in which the cumulative beam from all of the individual antenna elements is transmitted, and the characteristics of the radiation pattern of the array. Analysis of the amplitudes and phases of return beams of electromagnetic energy detected by the individual antennas in the array similarly allows determination of the direction from which a return beam arrives.
In communication systems, radar, direction finding and other broadband multifunction systems having limited aperture space, it is often desirable to efficiently couple a radio frequency transmitter and receiver to an antenna having an array of broadband radiator elements. For many antenna array applications, it is further desirable that the radiating antenna elements have low losses (e.g. low RF loss), operate across a wide frequency band of interest, and be inexpensive to fabricate. Several concepts have been investigated to provide radar or communications coverage over more than one frequency band using a single integrated array antenna.
With dedicated radar bands such S-Band and C-Band; C-Band and X-Band, for example, many of which are separated by nearly an octave or more of bandwidth, the selection of a radiating element becomes problematic due at least in part to difficulty in providing a suitable impedance match and element radiating pattern over both bands and the scan volume. A single element type may be impedance matched over one frequency band or the other band, but cannot adequately cover both bands. Similarly, a single element type may provide an adequate element radiating pattern over one frequency band, but exhibits nulls (i.e. minima) in the element radiating pattern in the other frequency band that represents a “blind” scan angle for the array.
Moreover, variations in dipole construction have not yielded a structure that provides both sufficient bandwidth and physically configurable within an element grid of a conventional radar array. While it is known that certain broadband elements such as notch antennas having flared or tapered notch antenna elements may be useful in forming wideband antenna arrays, dual band antenna array systems often require active switching, multiple apertures, and complex impedance matching that undesirably affect performance and usefulness of the device.
A system and method which overcomes the aforementioned difficulties is highly desired.